本論文旨在研製一高升壓比隔離型主動箝位順向/返馳式轉換器。二次側採
用電壓提升技術，以實現高升壓比。主動箝位電路用於回收順向/返馳式變壓器
漏電感能量，以降低開關元件電壓應力。藉由使用主動箝位電路並將電路操作於
邊界導通模式，一次側主開關與輔助開關皆可達到零電壓切換的特性。同時使用
固定截止時間改變頻率的方式減少變壓器鐵心損失，達到高轉換效率。主開關是
否可達到柔性切換與輸入電壓、輸出負載量無關，且不會增加額外的導通損。
本文將分析與討論電路之動作原理及設計，並實作一台輸入直流電壓24 V、
輸出直流電壓400 V/150 W之高升壓比隔離型主動箝位順向/返馳式轉換器，以驗
證理論分析與實測結果。

The thesis presents an isolated high step-up forward/flyback active-clamp
converter with output voltage lift. In order to obtain high step-up voltage gain, the
output voltage lift is adopted. The characteristics of the output voltage lift are similar
to the forward converter operates charging mode. The flyback converter operates
discharging mode.The active-clamp circuit is employed to recycle the
leakage-inductance energy of the forward/flyback transformer and to suppress the
voltage stress on the switch. By utilizing the active-clamp circuit, both primary and
auxiliary switches can achieve zero voltage- switching (ZVS), thus improving the
efficiency of the proposed converter. Lossless switching of the main switch
independent of the line and load conditions no increase in conduction losses, simple
power and control circuitry, and capability of operating in either voltage or current
mode control.
The converter operates at boundary mode between current continuous and
discontinuous mode to achieve ZVS. Variable frequency with fixed off time is used for
reducing core losses of the transformer, achieving high efficiency. Meanwhile, power
distribution between forward and flyback is analyzed as well. Finally, a prototype
circuit with 24-V input voltage, 400-V output voltage, and 150-W output power is
implemented to verify the performance.

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